Downloaded books getting offloaded from Books app on iPad mini.

My books keep getting offloaded from the Books app. I’ve been reading on Books for nearly a decade now, but about a few months back, my books kept getting offloaded and I would have to download them back again. I understand this is due to iCloud, and has to do with device storage but I have well over 30GB or so to spare, and I’m getting tired of downloading my hundreds of books again and again when I wanna read them. How do I solve this?

[Re-Titled by Moderator]